Calutron



Patented June 16, 1959 United States Patent Qfifiee CALUTRON WilliamParkins, Los Angeles, Calif., assignor to the United States of Americaas represented by the United States Atomic Energy Commission ApplicationJuly 23, 1946, Serial No. 685,645

Claims. (Cl. 250-413) This invention relates to magnetic devices formoving mechanical elements, and the invention is illustrated herein asapplied to a device, known as a calutron, for separating isotopes on ascale yielding commercially useful quantities of the separated material.For a complete disclosure of a calutron and its mode of operation,reference is made to U.S. Patent No. 2,709,222 which issued to Ernest 0.Lawrence, on May 24, 1955, for Methods of and Apparatus for SeparatingMaterials.

As disclosed in the above-mentioned Lawrence patent, a presentlypreferred form of the calutron comprises an evacuated tank disposedbetween the poles of an electromagnet so that the evacuated space withinthe tank is pervaded with a substantially uniform magnetic field of highflux density. Within the tank, there is provided a source unit adaptedto project a beam of positive ions of a polyisotopic charge materialalong an arcuate path extending transversely through the magnetic field,whereby the paths of ions of different mass are caused to diverge towardrespective foci disposed 180 along the arcuate beam path from the sourceunit. A receiver, also disposed within the tank, is positioned at the180 foci of the streams of ions of diiferent isotopes for separatelycollecting the component particles of one or more of those streams.

The receiver of the calutron comprises aviewing face disposed in thepath of the beam for defining a separate beam delimiting slot for eachion stream from which the collection of material is desired, each suchslot being adapted to pass a delimited portion of the beam enriched withrespect to a particular isotope component; and a separate ion collectingpocket is disposed behind each such slot for receiving and retaining theparticles passing therethrough.

The principal components of a calutron ion beam form a wide, ribbon-likestream of particles, the stream being relatively thin where it leavesthe source unit, gradually increasing in thickness during the first 90of its arcuate travel, and then decreasing in thickness during thesecond 90 of its arcuate travel. The final thickness of the beam at the180 region of focus is substantially greater than the thickness at thesource unit, by virtue of the angle of divergence of ions of the samemass at the source unit and the normal divergence of streams of ions ofdifferent mass.

The principal components of the ion beam comprise particles ofappreciable mass that are caused to deviate very slightly from truearcuate paths by various electrical and magnetic conditions within thecalutron tank, which conditions cannot readily be completely controlledin practice. In addition, slight irregularities in the operation of asource unit are diflicult to prevent and, as a result, the ion output ofthe source unit tends to fluctuate slightly during itsoperation.

All of these abnormal conditions affect the orientation of the 180 focalpatterns of the beam, which should remain focused as accurately aspossible upon their respec tive receiving areas on the beam viewing faceof the receiver. More particularly, as a result of certain types ofabnormal conditions, the ribbon-like beam has; been observed to twist orprecess slightly in one direction or the other about a median path ofthe beam, thereby causing the focal patterns to rotate to the sameextent about respective axes, passing approximately through thegeometrical centers of the focal patterns in the direction of travel ofthe beam at the 180 region of focus. Such twisting or precession of thebeam destroysthe accuracy of focus of the focal patterns on theirrespective beam receiving areas of the receiver, which reduces theamount of material received, or causes excessive contamination of thatmaterial arriving at one of the beam receiving areas with material thatshould arrive at a different beam receiving area.

Accordingly, it is an object of the present invention to provide, in acalutron, apparatus for moving the receiver so that the beam receivingareas thereof follow the shifting of the foci of the beam.

More particularly, it is an object of the invention to provide apparatusthat is responsive to the shifting of the foci of a calutron ion beamfor automatically moving the receiver so as to maintain a proper focusof the beam thereon during operation of the calutron.

Still other objects and advantages of the invention, and the manner inwhich the desired ends may be accomplished, will appear from thefollowing description of the invention, taken in conjunction with theaccompanying drawings, in which:

Figure 1 is a perspective view of a calutron tank having certain wallportions thereof broken away to disclose the arrangement therein of asource unit and a receiver, and the manner in which a beam travelsthrough the tank from the source unit to the receiver;

Fig. 2 is a vertical sectional view of the receiver shown in Fig. 1,illustrating the manner inwhich the receiver is rotatably mounted on asupporting tube; and

Fig. 3 is an elevational view of the receiver shown in Fig. 1, lookingat the beam viewing face thereof and showing how the receiver rotates tofollow the shifting of the beam received thereby.

Referring now to the drawings, a calutron tank 11 is shown with part ofits defining walls broken away to expose the apparatus containedtherein. The tank is mounted between a pair of vertically spaced-apartpole faces 12 (only one being shown) of an electromagnet to maintain amagnetic field of high flux density directed upwardly throughout theinterior of the tank from one pole face of the magnet to the other. Asource unit 13 is mounted on a wall of the tank at one end thereof forprojecting a beam of positively charged ions of a polyisotopic materialtransversely through the magnetic field along an arcuate path toward anion receiver 14 mounted on the same wall of the tank at the opposite endthereof. The receiver is rotatably supported by means of a bearing 16 ona tube 17 that projects through a suitable seal 18 in the wall of thetank on which the receiveris mounted, whereby the receiver may berotated about the axis of the tube 17 and the tube may be axially movedto position the receiver properly with respect to the beam to bereceived thereby.

The beam transmitted from the source unit 13 is of the type hereinbeforedescribed comprising separate streams of ions of dilferent isotopes (thestreams overlap to a considerable extent), the beam having a uniform,substantial height or width from end to end but varying in thickness. Atthe receiver, the beam components, by virtue of their divergence duringtravel from the source unit, have combined focal patterns that spreadover a considerable area of a viewing face 19, pfithe receiver 3 Slots21 and 22 may be provided in the viewing face 19 for admitting into theinterior of the receiver selected portions of two of the isotope ionstreams. In the present instance, employing a suitable uranium chargematerial inthe source unit 13, the' beam may be focused on the receiver14' so that a selected portion of maximum intensity of the stream" of Uions will pass through the.

slot 21 and a selected portion of maximum intensity of the stream of U?ions will pass through the slot 22. Since the U portion of the beam isby far the most intense portion, it is employed in the manner describedhereinafter for actuating a receiver aligning mechanism to maintainalignment of the receiver with the beam when the beam twists in themanner described above. The ver-' tical axis of this portion of thebeam, at all points along its length, is schematically illustrated inFig. 1 by an arcuately curved surface 23 extending from the source unit13" to the slot 22 in the receiver viewing face. In other words, thearcuately curved surface 23 represents the locus of U ion paths that lieon the vertical or major axis of the beam from end to end thereof.

Referring now to Fig. 3, the vertical axis of the U portion of the beamat the receiver is represented by the line 26. Because of the tendencyof the beam to rotate or twist about a median path thereof, the verticalaxis of the beam tends to twist in one direction or the other toaposition such as is represented by the line 260. When this occurs, it isnecessary to rotate the'rec'eiver about the axis of the tube 17 inorderto maintain alignment of the slots 2 1*and' 22 with the foci of'the Uand U components of the beam, respectively. To eflect such movementof'the'receiver automatically, a device such as the one nowtohe-described, is mountedbn the receiver in the path of the beam and inthe magnetic field pervading the interior of the tank'for cooperatingwith the U portion of the beam to rotate the receiver in response totwisting or shifting of the beam.

Four somewhat elongated pieces of magnetically permeable material 27 arerigidly secured to the viewing face 19 ofthe' receiver in any suitablemanner for rotation therewith about the axis of the supporting tube 17.These magnetic pieces are disposed'symmetrically with respect to th'e Uslot 22 with the'magnetic axes of each pair of diagonally oppositepieces'aligned; andwith diagonal Iines ZS defined by the'axesof themagnetic pieces intersecting directly in front of the geometrical'centerof the m net. The material from which'the magnetic pieces are madeshould be one having a high magnetic per-' meability that drops sharplyata predetermined elevated temperature, such as 'Kovar (a well known,substantially carbon-free alloy" of iron, cobalt, and nickel); and thepieces should be so located'that they are normally heated by the: beamto temperatures slightly-below the critical' temperature at which theylose their magnetic permeability.

By properly selecting the 'sizeof the magnetic pieces 27 with respect totheintensity of the portions'of thebeam bywhichthey will normally bebombarded (determined by their positions on the viewing face 19 "and thevarious" characteristics of thebeam), it is possible to create acondition of magnetic'equilibri-um when the vertical axis of'the U slotis accurately aligned with thevertical or major-axis 26 of the-U portionofthe beam at the receiver. If the beam twists sons to bring itsvertical axis to the position-indicated by thelin'e'ZtEa, it is appar-'ent that a diagonally opposite pair of magnetic pieces 27 will besubjected to stronger than normal'ion bombardment and that thetemperature ofthis'pair of magnetic pieces willbe raised accordingly.When the temperature a of this .pair of magnetic pieces 'rises above thecritical neticequilibrium; The entirerecei'ver will then be caused to.rotate about the tube 17 in a direction to bring the otherapair otdiag'onally 'opposite magnetic pieces 27 more 4 nearly into alignmentwith the calutron magnetic field. Such rotation of the receiver movesthe magnetic pieces toward positions of symmetry with respect to theshifted major axis of the beam, thereby eliminating the condition thatcaused excessive heating of one pair of magnetic pieces. As long as thebeam remains in its twisted position, any tendency for the receiver torotate back to its normal position will cause the above describedcondition of normal heating of the magnetic pieces to reoccur, therebycounteracting such tendency; While the arrangement may be inclined tooscillate back and forth somewhat before reaching a new position ofequilibrium appropriate for reception of the twisted beam, the newposition of equilibrium will be reached in a reasonably short time.

From the foregoing description, it will be appreciated that I haveprovided means for moving a receiver automatically to maintain the beamreceiving areasthereof in alignment with the foci of a calutron ion beamas the beam. twists about a median path thereof. However, it is to beunderstood that the invention is not limited to the' particularapparatus or to the particular type of use disclosed herein, but isapplicable to a variety of problems. Accordingly, the true spirit andscopeofithe invention is intended to be coextensive with the terms ofthe appended claims.

What is claimed is;

1. In apparatus including a target and means for projecting aribbon-likebeam of charged particles toward the'target, said beam beingcharacterized by a tendency" to'precess and thereby" to shift out offocus with targetyrneans associated with the target and respons ve:

to the precession of the beam for effecting a correspond ing rotation oftheQtarget.

2. Apparatus as defined in claim 1 including' mean's mounting saidrotatable target for movement substantially tangentially of said beampath.

3. In apparatus including a movable target and means rm projecting aribbon-like beam of charged particles; toward the target, said beambeing characterized by atendency to precess and thereby to shift out offocus" with the target; means mounted on the target in the path of thebeam and responsive to the precession of the beam for effecting acorresponding rotation of the target. g

4. In apparatus including a magnetic field, a target disposed in saidmagnetic field, and means for project ing aribbon-like beam of chargedparticles through said magnetic field toward said target, said beambeing" characterized bya tendency to precess and thereby to'shift" outof focus with the target; means mounted on the" target and operative inresponse to the precession of the beam for cooperating with the magneticfield 'to' effect a corresponding rotation of the target. 4

5. In apparatus including a magnetic field, means for projecting' a beamof charged particles through said magnetic field, and an element tobe'rotated re'spoiis'e" to changing beam conditions; means mounted inthe'l path of said beam and operative in response to changing beamconditions for rotating said element.

6. In apparatus including a'm'agnetic field, eansror projecting a beamof charged particles through 'said magnetic field, and an element to berotated in response to changing beam conditions; means mounted in thepath of the beam andoperative in response to changing' beamf conditionsfor cooperating with the magnetic field toeffect'rotation of saidelement. 4 7. Inapparatus including'a magneticfieldgmeansftor"projecting a beam of charged particles through said mag;

a predetermined path under the influence of said magnetic field when themagnetic permeability of the member changes.

8. In apparatus including a magnetic field, a target disposed in saidmagnetic field, and means for projecting a ribbon-like beam of chargedparticles through said magnetic field toward said target, said beambeing characterized by a tendency to precess and thereby to shift out offocus with the target; means disposed in the path of the beam andsubject to heating at a rate dependent upon the position of the beamwith respect thereto, said means being operative in response tovariation in its temperature for rotating the target to compensate forshifting of the beam.

9. Apparatus as defined in claim 8 wherein said means subject to heatingby said beam comprises a plurality of metallic pieces arranged in spacedrelation upon one face of said target.

10. In apparatus including a magnetic field, a target disposed in saidmagnetic field, and means for projecting a ribbon-like beam of chargedparticles through said magnetic field toward said target, said beambeing characterized by a tendency to precess and thereby to shift out offocus with the target; means disposed within said magnetic field and inthe path of the beam and subject to heating at a rate dependent upon theposition of the beam with respect thereto, said means being operative inresponse to changes in its temperature for cooperating with saidmagnetic field to maintain the target in focus with the beam as itprecesses.

References Cited in the file of this patent UNITED STATES PATENTS2,300,882 Ferguson Nov. 3, 1942

